What is the difference between water-based and solvent-based anti-fog lens coating?
Water- and solvent-based anti-fog coatings interact differently with many of the environmental conditions that produce the "fogging effect." They also react differently with exposure to chemical agents (although with any type of exposure, the wearer should immediately seek treatment and safely dispose of the eyewear). The most popular water-based anti-fog coatings are considered super hydrophilic (water-absorbing) and are generally applied at a thickness of 10 to 12 microns. Solvent-based coatings are also hydrophilic (usually 4 to 7 microns in thickness) but contain a couple of chemical agents you might not want to come in contact with or be exposed to: diacetone alcohol and toluene. Both of these chemicals can cause severe eye and skin irritation, and exposure to toluene can be more toxic than benzene, according to the CDC.
Both water- and solvent-based products are effective at preventing fogging in initial contact with a fogging event; however, lab testing shows that the thicker, water-based coating will last up to ten times longer in high humidity environments (up to 80C or 176F). Because the water-based coating is thicker, it can withstand cleaning significantly longer as well. Both should only be cleaned with water and a lint-free cloth.
Water is also, of course, environmentally friendly and entirely safe. Solvents have toxic properties, can be flammable, and can have a negative impact on the natural environment. Water-based coatings, on the other hand, are non-flammable and non-toxic.
When choosing safety eyewear, consider those that offer a water-based, hydrophilic coating. Also look for other important features. Try to purchase safety glasses that are washable, have UVA/UVB protection, and are lightweight and comfortable to wear, even for extended periods of time.
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